There are two principal goals for this project: 1) Elucidation of respiratory muscle function in normal subjects and in patients with respiratory disease, particularly those with respiratory disability and failure owing to chronic obstructive lung disease. 2) Development and evaluation of an analog computerized modification of the forced oscillation method of measuring respiratory resistance and net reactance at multiple frequencies as a means of detecting early obstructive disease of small airways. Respiratory muscles are being studied using several methods including electromyography, radiographic estimates of muscle lengths, configurations and contraction velocity, pressure measurements, and respiratory magnetometer measurements of changes in thoraco-abdominal dimensions and configurations. Data are being analyzed with reference to the length-tension and force-velocity characteristics of skeletal muscle. The computerized forced oscillation technique allows one conveniently to assess frequency dependence of resistance which should reflect unequal time constants of terminal lung units (owing to early small airway disease) in the same way frequency dependence of compliance does. The same can be said of frequency dependence of net reactance, the algebraic sum of the mechanical effects of respiratory compliance and inertance. The method will be tested in subjects identified by other methods as having early small airway obstruction.